1. Field of the Invention
This invention relates to aluminum alloy sheet products and methods for making such products. More particularly, the invention relates to a method for making aluminum foil products having improved surface characteristics, i.e., substantially no pinholes or streaks, with high burst strengths, bulge heights, ultimate tensile strengths and percent elongations at thin gauges.
2. Technology Review
Aluminum sheet products have been made for many years from numerous alloy compositions. End use applications for such products include: radiator and air conditioning finstock in the transportation industry; insulation panel backings in the building trade; closures, including lids and glassware screwtops: and other packaging needs such as household foil and semi-rigid containers. Rolled aluminum sheet may also be used for lithographic plate substrates, electronic condensors and etching foils.
Surface appearance is as critical as tensile strength in many of the foregoing applications. A stronger alloy would not be useful if it produces surface streaks or an unacceptable number of pinholes when rolled to a thin gauge. Conversely, bright and shiny product surfaces serve no purpose on sheet product with deficient tensile strengths. Many of the foregoing characteristics are impacted by the way in which an alloy is heat treated after, or sometimes between, roll reductions. Intermediate gauge products must possess the necessary elongation levels for withstanding repeated passes through today's complicated roll stand arrangements.
It has been known for some time to make rolled sheet product from such alloys as 1145, 1200, 8006, 8011, 8014 and 8079 aluminum (Aluminum Association designations). It has also been known to subject such products to a variety of heat treatment, and annealing conditions for maximizing one product characteristic, usually at the expense of another.
In U.S. Pat. No. 4,483,719, there is claimed a process for making fine-grained aluminum alloy sheet by cooling and annealing within preferred temperature ranges. The alloy consists essentially of: 0.8-1.5 wt. % iron; up to 0.5 wt. % manganese; up to 0.5 wt. % silicon; up to 0.3 wt. % of any one impurity, the total impurities level not exceeding 0.8 wt. %; and a balance of aluminum.
U.S. Pat. Nos. 4,800,950 and 4,802,935 show a lithographic plate substrate consisting essentially of 1.1-1.8 wt. % iron, 0.1-0.4 wt. % silicon, 0.25-0.6 wt. % manganese, up to 0.3 wt. % copper, up to 0.8 wt. % magnesium, up to 2.0 wt. % zinc and 1.0 wt. % of all other elements, each not exceeding 0.3 wt. % in total concentration, and a balance of aluminum. This substrate is cast to a thickness of 5-12 mm (0.2-0.47 inch) before annealing at 270.degree. C. (518.degree. F.) for 3 hours.
The anodized product of U.S. Pat. No. 4,806,211 comprises 1.2-1.6 wt. % iron, 0.25-0.55 wt. % manganese, up to 0.2 wt. % silicon, up to 0.3 wt. % copper, up to 5.0 wt. % magnesium, up to 0.1 wt. % chromium, up to 2.0 wt. % zinc, up to 0.25 wt. % zirconium, up to 0.1 wt. % titanium, up to 0.5 wt. % other elements and a balance of aluminum.
Japanese Patent No. 64-34,548 claims a method for making high strength foil from a composition containing 0.8-2 wt. % iron; at least one of: 0.1-1 wt. % silicon, 0.01-0.5 wt. % copper, 0.01-0.5 wt. % magnesium, 0.01-1 wt. % manganese; 0.1 wt. % or less titanium and/or 0.05 wt. % or less boron; and a balance of aluminum and impurities. This composition is cast to less than 3 mm (0.12 inch), then annealed at 200.degree.-450.degree. C. (392.degree.-842.degree. F.).
Despite the foregoing advancements, there is still need for: aluminum foil product that possesses a better combination of high strength and good surface characteristics; as well as improved methods for making such products. The present invention serves both needs.